This invention relates to a vibration damping device for suppressing vibrations of a brake in a positive manner in order to prevent squeals of the brake.
Means for suppressing squeals of a disc brake in a positive manner are disclosed e.g. in unexamined Japanese patent publications 4-54324 and 4-54325. A first piezoelectric element detects vibrations of the brake pads, and a second piezoelectric element applies vibrations to the pads based on the detection signals from the first piezoelectric element to damp the vibrations of the brake. The former publication '324 also discloses a vibration damper in which a vibrator applies inaudible vibrations to the friction members when the actuation of the brake switch is detected.
Such a conventional vibration damper of the type that detects brake vibrations through the pads and applies vibrations to the pads based on the vibration detection signal may be activated even while the brake is not applied if the pads vibrate due to whirling of the rotor. This occurs because the vibration damper mistakes the whirling of the rotor for brake vibrations. A vibration damper for a disc brake is designed to damp brake vibrations that can cause squeals of the brake. If, however, the vibration damper is activated due to vibrations of the kind that will not cause squeals of the brake (such as vibration induced by whirling of the rotor), it can increase, rather than decrease, vibrations that produce offensive noise. Such a damper practically does more harm than good.
Another type of conventional vibration damper is designed such that its circuit is activated only when the brake switch is on, so as to apply vibrations having a frequency out of the inaudible range to the pads. This damper has a problem in that it can be activated when not necessary, i.e. when the brake cannot squeal, such as when the driver is depressing the brake pedal with the vehicle at a stop.
A large amount of electric energy is needed to vibrate something at a high frequency. Thus, from an economical viewpoint, it is not desirable to vibrate the pads at a high inaudible frequency range as in the abovementioned prior art. Moreover, this conventional damper vibrates the pads when the brake switch is on, even if there is no necessity to apply vibrations to the pads, thus causing abnormal brake vibrations and offensive noise.
An object of this invention is to provide a solution to these problems.